The present invention relates generally to transmissions. More particularly, the present invention relates to planetary gear transmissions. Specifically, the present invention relates to the mechanisms for activating a brake and/or clutch used to control a planetary transmission.
A typical planetary gear transmission has components including at least one sun gear, at least one ring gear and a planet carrier with a plurality of planet gears rotatably mounted thereon, with the planet gears engaging one of the ring gears and/or one of the sun gears. It is known in the art to connect the input and output of the planetary gear transmission to varying combinations of the sun gears, the planet carrier, or the ring gears, depending upon the precise transmission characteristics desired. The typical planetary gear transmission is shifted between different gear ratios by using a clutch to connect pairs of one of the sun gears, planet carrier, or one of the ring gears against relative rotation, and/or by using a brake to fix one of the sun gears, the planet carrier or one of the ring gears against rotation relative to the transmission housing.
When both a clutch and a brake are used, a common control mechanism is typically a spring-biased hydraulic piston to control the brake and a separate spring-biased hydraulic piston to control the clutch. Depending upon the exact characteristics desired, the springs for the pistons can either bias the corresponding components into engagement or out of engagement, with hydraulic fluid being then applied to the piston to disengage or engage the component, as desired.
In most situations, it is undesirable to completely simultaneously engage the brake and clutch. Accordingly, when separate spring-biased hydraulic pistons are used to control the clutch and the brake, the timing of application of hydraulic fluid to the pistons for the two control mechanisms must be carefully controlled. Thus the control valve structure for these fluids must be very precisely designed and manufactured to ensure that this timing is correct.
Previously it has been known as an alternative to use a single piston to control both the clutch and brake. In such mechanisms a piston is spring biased to engage one of the components (clutch or brake) and disengage the second component, and hydraulically activated to disengage the first component and engage the second component, such that the brake and clutch will not both be completely engaged at the same time. However, it is still generally necessary that the clutch and brake never be fully disengaged simultaneously, or, if they must be, that they both be disengaged for very short time. In transmissions of the type discussed above, if the clutch and brake are disengaged and there is a load on the output while power is supplied to the input, the output will stop rotating. The result is that the component to which the brake is connected will rotate at a very high rate of speed. In some cases, depending on the gear ratios and the strength of the parts, among other things, the component to which the brake is connected (or rotating parts attached to it) can fail due to the loads imposed by centrifugal force.
Thus it is desirable that the engaging element start engaging before the disengaging element becomes fully disengaged. One conventional method for minimizing the time that a clutch and brake will be simultaneously disengaged involves a transmission where both the clutch and brake are engaged by separate pistons using fluid pressure to engage its associated clutch or brake. A control valve is manually controlled by the operator, introducing a risk that the valve will be moved slowly, resulting in the possibility that both clutches will be simultaneously engaged or disengaged. To avoid this occurrence, a second valve is used. The valve controlled by the operator controls only the second valve, which then directs fluid pressure to the appropriate clutch or brake. The second valve is strongly detented in each of two positions so that once it starts moving, it will complete its travel very rapidly. This serves to minimize but not eliminate the time that the clutch and brake will be simultaneously engaged or disengaged. In addition, this method involves the use of more than one piston to activate the clutch and brake.
A second conventional method for minimizing simultaneous disengagement of a clutch and brake is to use a spring to engage either the clutch or brake. This spring-engaged clutch or brake is disengaged by a piston activated by fluid pressure. The other clutch or brake is engaged by a second piston activated by fluid pressure. Fluid pressure is applied to or released from both pistons simultaneously, as fluid is supplied by one valve to both pistons. This provides relatively dependable phasing of the clutching elements during the shift, but requires multiple pistons and carefully designed control valves.
Accordingly, there is a clear need in the art for a transmission having a single actuator for simultaneously engaging/disengaging the clutch and brake.
In view of the foregoing, it is an object of the invention to provide a mechanism which can fully activate only one or the other of the brake and clutch of a planetary transmission at a time, without requiring overly cumbersome design and manufacture of control valves for the structure.
Another object of the invention is the provision of such a mechanism which ensures that the clutch and brake are not fully deactivated simultaneously.
A further object of the invention is to provide a two-speed planetary transmission with shifting activated by a single, non-rotating piston.
The foregoing and other objects of the invention together with the advantages thereof over the known art which will become apparent from the detailed specification which follows are attained by a planetary gear transmission comprising: a transmission housing; a sun gear mounted in the housing; a ring gear mounted in the housing; a planet carrier mounted in the housing; at least one planet gear rotatably mounted to the planet carrier and engaged with the sun gear; at least one planet gear rotatably mounted to the planet carrier and engaged with the ring gear; a brake for selectively braking one of the sun gear, the ring gear and the planet carrier against rotation relative to the transmission housing; a clutch for selectively clutching together two of the sun gear, the ring gear and the planet carrier to prevent relative motion therebetween; an actuator coupled to the brake and the clutch, the actuator movable between a braking position wherein the brake is fully engaged and the clutch is fully disengaged, a clutching position wherein the clutch is fully engaged and the brake is fully disengaged, and a plurality of intermediate positions wherein at least one of the clutch and the brake is always at least partially engaged.
Other objects of the invention are attained by a planetary gear transmission comprising: a housing having a piston chamber, the piston chamber being in fluid communication with a source of fluid pressure; input and output shafts rotatably mounted in the housing; a planet carrier coupled to one of the input and output shafts for rotation therewith; a set of compound planetary gears rotatably carried by the planet carrier, each compound planetary gear of the set of compound planetary gears comprising first and second planet gears rotatable about a common axis and fixed against rotation relative to each other, the first and second planet gears forming first and second planetary gearsets; a ring gear encircling the set of compound planet gears and meshing with one of the first and second planet gearsets, the ring gear coupled for rotation with the one of the input and output shafts to which the planet carrier is not coupled; a sun gear mounted for rotation about one of the input and output shafts and meshing with one of the planet gears; a clutch engageably and disengageably coupling the sun gear for rotation with the one of the input and output shafts to which the planet carrier is coupled; a brake engageably and disengageably fixing the sun gear against rotation relative to the housing; a piston mounted in the piston chamber and slidable in response to fluid pressure between an engaged position for engaging one of the clutch and the brake and a retracted position for disengaging the one of the clutch and the brake.
Still other objects of the invention are attained by a planetary gear transmission comprising: a transmission housing; a sun gear mounted in the housing; a ring gear mounted in the housing; a planet carrier mounted in the housing; an input shaft connected to the ring gear; an output shaft connected to the planet carrier; at least one planetary gear rotatably mounted to the planet carrier and engaged with the sun gear; at least one planetary gear rotatably mounted to the planet carrier and engaged with the ring gear; a clutch drum connected to the sun gear, the clutch drum having first and second sides, the first side having a friction disc affixed thereto; a clutch pressure plate connected to the clutch drum, the clutch pressure plate having first and second sides, the second side having a friction disc affixed thereto; a clutch backing plate connected to the clutch drum, the clutch backing plate having a plurality of apertures therein, the clutch backing plate also having first and second sides, the first side having a friction disc affixed thereto; a clutch disc interposed between the second side of the clutch pressure plate and the first side of the clutch backing plate and affixed to the output shaft; a clutch release plate having first and second sides with a plurality of projections extending from the first side, the plurality of projections matingly engaging the plurality of apertures in the clutch backing plate and extending therethrough, the clutch release plate also having a friction disc affixed to the second side thereof; a housing extension rigidly affixed to the housing and interposed between the planet carrier and the first side of the clutch drum; a piston cavity formed in the housing, the piston cavity having a hydraulic passage in fluid communication with a source of fluid pressure; a piston slidably disposed in the piston cavity, the piston having a contact face opposing the friction disc and second side of the clutch release plate; a clutch apply spring interposed between the second side of the clutch drum and the first side of the clutch pressure plate; and, a brake return spring interposed between the first side of the clutch drum and the planet carrier; whereby the clutch pressure plate is biased into engagement with the clutch disc by the clutch apply spring and when pressurized hydraulic fluid is introduced into the piston cavity, the piston is moved into engagement with the clutch release plate at which point the projections extending through the clutch backing plate engage the clutch pressure plate thereby overcoming a bias force provided by the clutch apply spring and moving the clutch pressure plate out of engagement with the clutch disc and simultaneously moving the clutch drum into engagement with the housing extension to provide braking of the sun gear thereby slowing the planet carrier and the output and when fluid is drained from the piston cavity the brake return spring moves the clutch drum out of engagement with the housing extension and simultaneously the clutch apply spring moves the clutch pressure plate back into engagement with the clutch disc causing all elements of the transmission to rotate at the same speed resulting in a direct drive.
In general, a planetary gear transmission is provided having a sun gear, ring gear and planet carrier mounted in a housing. A plurality of compound planet gears are rotatably mounted to the planet carrier. The planet carrier is connected to one of either an input shaft or an output shaft while the ring gear is connected to the other of either the input shaft or output shaft. A clutch engageably and disengageably couples the sun gear for rotation with one of the input or output shafts to which the planet carrier is coupled. A brake engageably and disengageably fixes the sun gear against rotation relative to the housing. A hydraulically engaged/spring disengaged non-rotating piston is mounted in the housing and is slidable in response to fluid pressure between an engaged position for engaging one of the clutch and the brake and a retracted position for disengaging the one of the clutch and the brake. Whereby the transmission operates in a first range when the clutch is engaged and the brake is disengaged and operates in a second range when the brake is engaged and the clutch is disengaged.
To acquaint persons skilled in the art most closely related to the present invention, one preferred embodiment of the invention that illustrates the best mode now contemplated for putting the invention into practice is described herein by and with reference to, the annexed drawings that form a part of the specification. The exemplary embodiment is described in detail without attempting to show all of the various forms and modifications in which the invention might be embodied. As such, the embodiment shown and described herein is illustrative, and as will become apparent to those skilled in the art, can be modified in numerous ways within the spirit and scope of the inventionxe2x80x94the invention being measured by the appended claims and not by the details of the specification.